The present invention generally relates to a microwave tube for use in amplification of microwave signals such as a klystron or travelling wave tube, and more particularly, to shielding means for a microwave tube having a structure in which a body section and a collector section are electrically isolated from each other.
Microwave tubes typically are comprised of a body section including a slow wave circuit or a cavity for achieving an amplification through an interaction between an electron beam and an input signal wave and a collector section for eventually capturing the electron beams. Recently, one type of microwave tube which is presently being manufactured in large quantities and is in widespread use, is designed to have a configuration such that the body section and the collector section are insulated from each other by a ceramic seal, enabling body current and collector current to be individually measured and also for the purpose of providing high operating efficiency by the application of a reduced voltage to the collector section with respect to the body section. However, the present day techniques employed for insulating the body section from the collector section as described above, have been found to create a disadvantageous condition wherein microwave energy has been found to leak out of the tube through the insulating portion and be fed back to an input portion of the tube, resulting in degradation of the tube performance and, in the worst case, resulting in undesirable oscillation.
Furthermore, in the case of a high power tube, a health risk is involved in that the body of an operator is subjected to the adverse effects of the leaked microwave energy at the time of the adjustment of the tube. The leakage of microwave radiation must, therefore, be reduced to a safe level.
Heretofore, as a solution for the aforementioned problem, it has been proposed to provide a structure in which the length of the gap space in the insulating portion is selected to be equal to 1/4 wavelength or 1/2 wavelength measured at the operating frequency of the tube, in order to form a choke, but this structure involves a problem in manufacture with respect to the dimensions required to achieve the aforesaid objects.
Another proposal contemplates the shielding of a leaked microwave signal by covering said insulating portion with a metallic shield body having its one end connected to the body section and having the gap space for insulation arranged between the other end thereof and the collector section so that said gap space is made as narrow as possible. However, when it is intended to apply this shielding means to the above-referred depressed collector potential type of microwave tubes in which a voltage of thousands to tens of thousand volts is applied across the insulating portion, the gap space for insulation cannot be made too narrow is view of the necessity for providing a minimum level of withstanding voltage, and accordingly, the leakage of microwave energy through the gap space cannot be neglected, making the provision of perfect shielding impossible in present day devices.